Ink jet recording is a printing method in which ink droplets are ejected and made to adhere to a recording medium (e.g., paper). Ink jet recording technology has advanced such that ink jet recording is now used for high-precision printing such as photographic quality printing, which previously was exclusively performed using silver halide photography or offset printing. High-precision ink jet recording has led to the development of ink jet recording media having high gloss relative to standard photographic paper. The recording media used in high-gloss ink jet recording typically include a porous ink receiving layer comprising a pigment (e.g., silica) and a binder coated over a substrate (e.g., paper or film).
Ink used for printing on the above-described high-gloss recording media are typically water-based and include colorants, resin components, and various other additives. Either dyes or pigments may be used as colorants. However, pigments are preferred due to the superior resulting print quality and improved permanence.
Due to color variations in a typical print the recording medium onto which the ink is applied includes areas with relatively more ink than other areas—in fact, some areas of the recording medium may have no ink applied at all. When using pigment-based inks, a glossiness of a resulting print may vary as a function of the amount of ink applied to the recording medium. Consequently, the areas of the recording media having relatively more ink appear different in gloss than the areas of the recording media having relatively less (or no) ink. This difference in gloss, called differential gloss, can be objectionable to the viewer of the printed output.
A further problem when printing with pigment-based inks is referred to as chromatic gloss. Chromatic gloss is the colored appearance of reflected white light. This may be viewed as objectionable to the user.
One method of overcoming these drawbacks is to apply a colorless ink over the colored inks on the recording medium on top of (i.e. after) all of the colored pigmented inks have been applied. Conventionally, applying a colorless ink in this manner has been accomplished by a multi-step process in which the recording medium is passed through a printing apparatus multiple times. For example, the recording medium is passed through the printer a first time during which all of the colored inks are applied to the recording medium. Then, the recording medium is passed through the printer a second time during which the colorless ink is applied to the recording medium. Such a multi-step process may be undesirably time consuming.
To circumvent this reduction in productivity, printers may be designed to apply both the colorless and colored inks concurrently, thereby increasing the overall output. However, it has been observed that the colorless ink can adversely impact the shape of the dots of the printed colored ink on those occasions when the colored ink is applied on top of the colorless ink. The result of this change in dot morphology can give rise to an increase in perceived graininess and/or haze of the printed output. For example, it is preferable that the dots of the printed colored ink be substantially circular in shape. The charge in dot morphology using these prior methods results in a dot that is substantially deformed. Furthermore, the colorless ink is less effective at reducing differential gloss and chromatic gloss when it is not primarily applied on top of the colored inks.
The present invention provides a new and improved method which addresses the above-referenced problems.